1. Technical Field
The entire disclosure of Japanese Patent Application No: 2016-119199, filed Jun. 15, 2016 is expressly incorporated by reference herein in its entirety.
The present invention relates to a medium feeder that feeds a medium and an image reading apparatus having the medium feeder.
2. Related Art
In a scanner which is an example of the image reading apparatus, driving sources for various driving systems are provided inside the apparatus main body.
For example, in JP-A-4-242234, a stepping motor is used as a driving source for driving an optical system of a copier machine.
A scanner may include a medium feeder (also called an auto document feeder (ADF)) that automatically feeds a document as a medium so that a plurality of documents can be automatically fed to an image reading unit which is fixed inside the apparatus and read by the image reading unit (for example, see JP-A-2014-60494).
Such a medium feeder provided in the scanner includes a feed roller that feeds a document loaded on a document tray, a transport roller that transports the document fed out from the feed roller to the image reading unit, and the like, and these components are driven by a driving source such as a motor.
When a stepping motor such as that described in JP-A-4-242234 is used as a driving source for the medium feeder that feeds a document to the image reading unit which is fixed inside the apparatus, there is a risk of disorder in transportation of the document which occurs if load of the driving source varies during scanning by the image reading unit, and this may cause a disturbance in the read image. In order to solve this problem, a DC motor may be used as a driving source of a medium feeder (for example, see JP-A-6-54132 and JP-A-2006-10855).
Since a DC motor is provided with an encoder, it can perform feedback control in response to variation in load of the motor, thereby easily reducing a disturbance of the read image which occurs due to variation in load of the motor.
For the scanners having such a medium feeder, more compact apparatuses are needed by users. However, a space for a driving source such as a motor which is relatively heavy and large is limited, and a layout for components is also limited.
In particular, as an example of a small-sized scanner, a scanner described in JP-A-2014-60494 has a housing that constitutes the scanner and is divided into an upper unit (cover 11b) and a lower unit (main body 11a). The upper unit is configured to be open relative to the lower unit for maintenance of the medium feeder or the like. In this case, the weight balance when the upper unit is open is an important matter.